Why Do Original Equipt Tires Rate So Low?

Why Do Original Equipt Tires Rate So Low on Sites like Tire Rack?


If vehicle mfgs work with tiremakers to design and build tires specifically for certain car/truck models, why do such tires often earn such low consumer ratings, particularly for wet, snow, and icy operations?

It isn't so much that the vehicle manufacturers work WITH the tire manufacturers as much as it is the vehicle manufacturers DICTATE the specs. And because fuel economy is so important to a vehicle manufacturer (and tire wear isn't!), vehicle manufacturers specify low rolling resistance values.

To get low RR values, the treadwear and/or traction (especially wet traction) gets sacrificed. And since the vehicle manufacturers don't provide a warranty on tires, unlike almost every other part of the car, the vehicle manufacturers can specify low RR values with impunity.

It isn't so much that the vehicle manufacturers
work WITH the tire manufacturers as much as it is
the vehicle manufacturers DICTATE the specs. And
because fuel economy is so important to a vehicle
manufacturer (and tire wear isn't!), vehicle manufacturers
specify low rolling resistance values.

To get low RR values, the treadwear and/or traction
(especially wet traction) gets sacrificed. And since the
vehicle manufacturers don't provide a warranty on tires,
unlike almost every other part of the car, the vehicle
manufacturers can specify low RR values with impunity.


Thanks!

So it should be good enough just to make sure the replacement tires match the OEM size and are equal to or greater with regards to load and speed rating.

Going from a regular(passenger) All Season - such as might be specified by the car maker - to a Touring or Grand Touring is probably a better idea than seeking out the exact make and model of tire that came on the car new.

Thanks!

So it should be good enough just to make sure the replacement tires match the OEM size and are equal to or greater with regards to load and speed rating.....

Good enough - Yes! But you should consider what you want the tire to do. If grip is a high priority, then you're going to sacrifice wear - and vice versa.

……. Going from a regular(passenger) All Season - such as might be specified by the car maker - to a Touring or Grand Touring is probably a better idea than seeking out the exact make and model of tire that came on the car new.

If one is satisfied with the OEM tire, by all means, do that.

But if one isn't, chose a tire that is more in tune with what your goals are.

But I get the sense that you think that there is some sort of quality improvement going from - say - an All Season to a Touring, then on to a Grand Touring. That is not the case.

These categories are to help you select a tire more appropriate to your needs - the scale being mostly about speed rating. The problem is that there are other things going on as well.

For example: The higher the speed rating, generally the lower the aspect ratio - and also, generally, the better grip and the harsher the ride. But there are enough exceptions to make this rule hardly a rule.

Good enough - Yes! But you should consider what you want the tire to do.
If grip is a high priority, then you're going to sacrifice wear - and vice versa.



If one is satisfied with the OEM tire, by all means, do that.

But if one isn't, chose a tire that is more in tune with what your goals are.

But I get the sense that you think that there is some sort of quality improvement
going from - say - and All Season to a Touring, then on to a Grand Touring. That
is not the case.

These categories are to help you select a tire more appropriate to your needs - the
scale being mostly about speed rating. The problem is that there are other things
going on as well.

For example: The higher the speed rating, generally the lower the aspect ratio - and
also, generally, the better grip and the harsher the ride. But there are enough
exceptions to make this rule hardly a rule.


The user ratings tend to be higher for tires that are the same size, load, and speed category, but have terms like "grand touring" or "performance all season" attached to their name or model number.

I've seen higher profile tires(60-70 series) as well as lower profile,(50-40 series) in the higher tier all season categories(touring, performance), so I don't sense that correlation - between touring and performance attached mainly to higher profile models.

The user ratings tend to be higher for tires that are the same size, load, and speed category, but have terms like "grand touring" or "performance all season" attached to their name or model number.

I've seen higher profile tires(60-70 series) as well as lower profile,(50-40 series) in the higher tier all season categories(touring, performance), so I don't sense that correlation - between touring and performance attached mainly to LOWER-profile models.

I meant lower-profile! darn!

When it comes to these performance categories, it's a trend, but there are enough exceptions to make it difficult to sort out.

In the old days, All Season tires were pretty much S and T rated and Touring tires were H rated, but high performance tires were V rated. Further, it used to be that high performance tires were stiff riding, All Season tires soft riding, and Touring tires in between.

Lots of changes since then. In particular, the Ford/Firestone thing back in 2000 pointed out the need for higher speed capability - that is, problem tires were all S rated, but H rated tires hardly had any failures. To insure that the tires coming from the vehicle assembly plant were of higher quality, the vehicle manufacturers started specifying higher speed ratings. However, the ride quality was specified at the same level as the S rated tires.

The good news is that ride quality isn't tied to the same tire components that speed rating is, so it was possible to get the same ride quality in a V and higher rated tire (albeit by sacrificing steering crispness.)

Nowadays we have a mixed bag, and while the tendencies are still there, it is a lot harder to see them.

When it comes to these performance categories, it's a trend,
but there are enough exceptions to make it difficult to sort out.

In the old days, All Season tires were pretty much S and T rated and Touring
tires were H rated, but high performance tires were V rated. Further, it used
to be that high performance tires were stiff riding, All Season tires soft riding,
and Touring tires in between.

Lots of changes since then. In particular, the Ford/Firestone thing back in 2000
pointed out the need for higher speed capability - that is, problem tires were all
S rated, but H rated tires hardly had any failures. To insure that the tires
coming from the vehicle assembly plant were of higher quality, the vehicle
manufacturers started specifying higher speed ratings. However, the ride quality
was specified at the same level as the S rated tires.

The good news is that ride quality isn't tied to the same tire components that
speed rating is, so it was possible to get the same ride quality in a V and higher
rated tire (albeit by sacrificing steering crispness.)

Nowadays we have a mixed bag, and while the tendencies are still there, it is a
lot harder to see them.


The "Ford/Firestone thing" had more to do with Ford specifying '60s-era pressures - 26PSI if I recall - for their then new Explorer utility, to counter vertical stability issues in that new platform. By 1990, a contemporary competitor, S10 Blazer, recommended 35psi cold at all four corners.

Running 26psi in any recent RAV4, Explorer, New Blazer, or Grand Cherokee, is almost begging for a blowout, even on just a long drive home from the dealer you picked it up from.

The "Ford/Firestone thing" had more to do with Ford specifying '60s-era pressures - 26PSI if I recall - for their then new Explorer utility, to counter vertical stability issues in that new platform. By 1990, a contemporary competitor, S10 Blazer, recommended 35psi cold at all four corners.

Running 26psi in any recent RAV4, Explorer, New Blazer, or Grand Cherokee, is almost begging for a blowout, even on just a long drive home from the dealer you picked it up from.

I go into great detail about this here: http://www.barrystiretech.com/fordfirestone.html

Bottomline: There was an identifiable cause for the tire failures - unique to the tires in question - AND - while the inflation pressure wasn't helping things, it was within the bounds of what was being done in the timeframe (where other vehicles and other tires did NOT have this problem)

So, No! The pressure specified by Ford was NOT the thing that caused the problem.

(Please note: The key to sorting this out is to look at the GAWR's and tire load carrying capacity at the pressure specified.)

I go into great detail about this here: http://www.barrystiretech.com/fordfirestone.html

Bottomline: There was an identifiable cause for the tire failures - unique to the tires in question - AND - while the inflation pressure wasn't helping things, it was within the bounds of what was being done in the timeframe (where other vehicles and other tires did NOT have this problem)

So, No! The pressure specified by Ford was NOT the thing that caused the problem.

(Please note: The key to sorting this out is to look at the GAWR's and tire load carrying capacity at the pressure specified.)


So are you suggesting that 26psi cold was an acceptable pressure, but that anticipated loads per axle weren't taken into consideration?

Confused..

So are you suggesting that 26psi cold was an acceptable pressure, but that anticipated loads per axle weren't taken into consideration?

Confused..

Let me put it like this:

Tires on the 1997-1999 Ford Explorer: *

P235/75R15 @ 26 psi = 1594# = size in question!!
P225/70R15 @ 30/35 psi = 1475#/1594#
P255/70R16 @ 30 psi =1913#

Tires on the 1997-1999 Chevy Blazer:

P205/75R15 @ 35 psi = 1452#
P235/70R15 @ 32 psi = 1643#

* - Tire load carrying capacities at the pressure specified INCLUDING adjustment for use on an SUV.

Please note that the load carrying capacity of the tire in question is NOT the lowest value.

I didn't show other vehicles, nor do I have the GAWR's, but at the time (Fall of 2000) I did ALL of the vehicles and had access to the GAWR's (which I don't now) and I gave that information to our VP of quality for the tire manufacturer I worked for. I was asked to do this to be sure we knew what was going on - particularly since Firestone was pointing out the pressure issue. Looks like they did a good job of obscuring the facts as the argument continues to sway people even 20 years later.

What did come out of this analysis was that - using our own data - certain tire combinations showed NO returns for the same time period - and those returns had one thing in common = H and higher speed ratings.

Our conclusion at the time was that it wasn't the pressure on the Ford Explorer that was the issue. I wasn't in a position (at the time) to know what the issue was (somebody in our organization did!), but I later found bits and pieces on the internet to get enough to make a coherent story - which lead me to write up the webpage I cited above.

So for 20 years I have been saying that the pressure was not the issue and the combination of the design of the tread pattern and the way the plant processed the rubber WERE the issue. This is also what the government (NHTSA) found.

Let me put it like this:

Tires on the 1997-1999 Ford Explorer: *

P235/75R15 @ 26 psi = 1594# = size in question!!
P225/70R15 @ 30/35 psi = 1475#/1594#
P255/70R16 @ 30 psi =1913#

Tires on the 1997-1999 Chevy Blazer:

P205/75R15 @ 35 psi = 1452#
P235/70R15 @ 32 psi = 1643#

* - Tire load carrying capacities at the pressure specified INCLUDING adjustment for use on an SUV.

Please note that the load carrying capacity of the tire in question is NOT the lowest value.

I didn't show other vehicles, nor do I have the GAWR's, but at the time (Fall of 2000) I did ALL of the vehicles and had access to the GAWR's (which I don't now) and I gave that information to our VP of quality for the tire manufacturer I worked for. I was asked to do this to be sure we knew what was going on - particularly since Firestone was pointing out the pressure issue. Looks like they did a good job of obscuring the facts as the argument continues to sway people even 20 years later.

What did come out of this analysis was that - using our own data - certain tire combinations showed NO returns for the same time period - and those returns had one thing in common = H and higher speed ratings.

Our conclusion at the time was that it wasn't the pressure on the Ford Explorer that was the issue. I wasn't in a position (at the time) to know what the issue was (somebody in our organization did!), but I later found bits and pieces on the internet to get enough to make a coherent story - which lead me to write up the webpage I cited above.

So for 20 years I have been saying that the pressure was not the issue and the combination of the design of the tread pattern and the way the plant processed the rubber WERE the issue. This is also what the government (NHTSA) found.


I ran the calculations using the formula posted elsewhere in this forum, assuming original size tire on a 2WD 1997 Explorer(using GAWRs from the placard image in the Barry's article you linked to).


Specifying the 2WD 1997 Explorer on TireRack, the recommended tire is 235/75R15, 105T, Max load 2,039lbs at Max cold pressure 44psi:

FRONT = 2,510/2 = 1,250/2,039 * 44psi = 26.97 cold (27)

REAR = 2,900/2 = 1,450/2,039 * 44psi = 31.28 cold. (31)

So the formula suggests significantly higher rear cold pressures, and only a slight bump up in the front pressures, presumably to maintain steering feel.


Most large legacy rear-drive vans(think: Econoline, Express, B2500), run at least that front-rear difference, if not at least 20psi higher rears than fronts.

I still implicate the low pressures on those Explorers as at least 60% of the culprit in those tread-sep/blow-out cases. Those cross-section photos(Figure 9) in the Barry's article could have been of any tire, from any vehicle or tire mfg. We'll never know definitively.

Low pressure was indeed a major culprit in this mess. Ford, themselves, are the ones who recommended the lower PSI because their models showed that the Explorer would be more likely to rollover at 35 PSI. The recommended 26 PSI was already very low, and with a propensity to lose 2 PSI a month, the possibility of getting to dangerously low PSI causing tread separation, and therefor the possibility of a rollover.

Low pressure was indeed a major culprit in this mess. Ford, themselves, are the ones who recommended the lower PSI because their models showed that the Explorer would be more likely to rollover at 35 PSI. The recommended 26 PSI was already very low, and with a propensity to lose 2 PSI a month, the possibility of getting to dangerously low PSI causing tread separation, and therefor the possibility of a rollover.


They recommended those lower pressures because a fresh-from-the-ground up suspension redesign would have been far more expensive than re-using the Bronco II-based platfrom under the 1st and 2nd-gen Explorers in conjunction with those low tire pressures. I would have drawn the line at 30psi.

It seems that making money was more important at Ford than a safe suspension with reasonable cold tire pressures.

I ran the calculations using the formula posted elsewhere in this forum, assuming original size tire on a 2WD 1997 Explorer(using GAWRs from the placard image in the Barry's article you linked to). ……

So first off, that formula is faulty. The formula used by the tire manufacturers is quite complex, which is why they publish charts - which is where I got my values.

Here's a version of that chart:

https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf

Yes, it is from Toyo tires, but the chart is the same regardless of who manufactures the tire. (and for completeness sake, there is some complication that makes it harder to understand. I go into more detail here):

http://www.barrystiretech.com/tirestandardizingorgs.html

…….. Specifying the 2WD 1997 Explorer on TireRack, the recommended tire is 235/75R15, 105T, Max load 2,039lbs at Max cold pressure 44psi: ……..

No, do not use the max pressure for anything other than the max pressure.

…...

FRONT = 2,510/2 = 1,250/2,039 * 44psi = 26.97 cold (27)

REAR = 2,900/2 = 1,450/2,039 * 44psi = 31.28 cold. (31)

…….

No, the 44 psi value is not tied to the 2039# value. The 2039 value is tied to 35 psi.

So if you use the correct 35 psi value, you get 21.46 psi front and 24.88 psi rear.

…… So the formula suggests significantly higher rear cold pressures, and only a slight bump up in the front pressures, presumably to maintain steering feel. …….

But if you use the correct values, it says the pressures were OK. Don't forget that the government (NHTSA) looked at all this and had the tires recalled, not the vehicle.

……. Most large legacy rear-drive vans(think: Econoline, Express, B2500), run at least that front-rear difference, if not at least 20psi higher rears than fronts. …..

2 thoughts:

First, those are vans, not SUV's

You are pointing out vehicles that use LT metric tires, Look up the base vans that used P type tires (E-150, B1500, etc.) and you'll find a different story.

….. I still implicate the low pressures on those Explorers as at least 60% of the culprit in those tread-sep/blow-out cases. Those cross-section photos(Figure 9) in the Barry's article could have been of any tire, from any vehicle or tire mfg. We'll never know definitively.

Those photos were in Dr. Govindjee's report and were published in the NHTSA EA00-023 report used to justify the tire recall. Are you implicating that NHTSA (and Dr. Govindjee's) didn't use photos of the tire in question when they had abundant samples available?

Oh, and I don't think you've yet realized that I am Barry.

So first off, that formula is faulty. The formula used by the tire manufacturers is quite complex, which is why they publish charts - which is where I got my values.

Here's a version of that chart:

https://www.toyotires.com/media/2125/application_of_load_inflation_tables_20170203.pdf

Yes, it is from Toyo tires, but the chart is the same regardless of who manufactures the tire. (and for completeness sake, there is some complication that makes it harder to understand. I go into more detail here):

http://www.barrystiretech.com/tirestandardizingorgs.html



No, do not use the max pressure for anything other than the max pressure.



No, the 44 psi value is not tied to the 2039# value. The 2039 value is tied to 35 psi.

So if you use the correct 35 psi value, you get 21.46 psi front and 24.88 psi rear.



But if you use the correct values, it says the pressures were OK. Don't forget that the government (NHTSA) looked at all this and had the tires recalled, not the vehicle.



2 thoughts:

First, those are vans, not SUV's

You are pointing out vehicles that use LT metric tires, Look up the base vans that used P type tires (E-150, B1500, etc.) and you'll find a different story.



Those photos were in Dr. Govindjee's report and were published in the NHTSA EA00-023 report used to justify the tire recall. Are you implicating that NHTSA (and Dr. Govindjee's) didn't use photos of the tire in question when they had abundant samples available?

Oh, and I don't think you've yet realized that I am Barry.

So always use 35psi in that formula?? What if we're doing calculations for LT rated tires?

Also, for the OEM size listed for my 2010 Accord - 225/50R17 93V, that size cannot even be found in 93V anymore. Only 94V or higher.

I just put a set of Pirelli P7 pluses on there, 94V: max load 1,477 @ 51psi max cold. Why on earth should I run the formula I ran using only 35psi as the max? Is the 44 or 51(in my case) max cold stamped on those tires 'fake' - or just for marketing?

Max is max. You shouldn't run max PSI, pretty much ever. It is simply the maximum pressure the tire could be inflated to. You should run what the vehicle manufacturer recommends.

Max is max. You shouldn't run max
PSI, pretty much ever. It is simply the maximum
pressure the tire could be inflated to. You should
run what the vehicle manufacturer recommends.

Please indicate wherever in this conversation I ever suggested running max cold pressure in ones tires.

The formula I indicated simply uses that max cold pressure as a basis to run the percentage off of, giving you an alternate cold pressure that could be lower, equal to, or higher than what is listed on your vehicle's TIP(Tire Info. Placard) sticker.

"You should run what the vehicle
manufacturer recommends"

You're preaching to the choir with that.

Sorry, I guess I misunderstood your question. I have had to argue with people before that insist the max psi is what you should run your tires at. I tried to explain to the one guy I work with how he was wrong and he argued "I used to sell tires I know what I am talking about." I simply replied, "Just because you sold tires doesn't mean you know what's right."

Sorry, I guess I misunderstood your question. I have had to argue with people before that insist the max psi is what you should run your tires at. I tried to explain to the one guy I work with how he was wrong and he argued "I used to sell tires I know what I am talking about." I simply replied, "Just because you sold tires doesn't mean you know what's right."


I do know that running max cold pressure, or even a few PSI below it, makes the steering all squirrelly and twitchy in the few cars I used to run it in, decades ago before I learned to read what was on that TIP sticker, lol!

Most of the cars I've driven since 2005 actually roll and accelerate better down near the pressures that the vehicle mfg. specifies, than at max on the tire. You'd think it would be the opposite, but nope! :)

So always use 35psi in that formula?? What if we're doing calculations for LT rated tires? ….

No, don't use that formula at all. Use a load table. That may require you to do some searching on the 'net to find one - and the good news is that it doesn't matter what tire manufacturer publishes the table, they are merely reproducing the table published by the tire standardizing organizations - which apply to every tire manufacturer.

..... Also, for the OEM size listed for my 2010 Accord - 225/50R17 93V, that size cannot even be found in 93V anymore. Only 94V or higher. ……

In this case you only need to find a table that has 225/50R17 in it. The load index and speed rating don't matter. (OK, there is one hiccup and that is you have to pay attention if the tire is SL (Standard Load) or XL (Extra Load)

Besides, the pressure listed on your vehicle tire placard is applicable to your vehicle regardless - unless you change tire size. (and here you can tell if your vehicle requires an XL tire if the specified pressure is over 35 psi - with a couple of exceptions.)

…….I just put a set of Pirelli P7 pluses on there, 94V: max load 1,477 @ 51psi max cold. Why on earth should I run the formula I ran using only 35psi as the max? Is the 44 or 51(in my case) max cold stamped on those tires 'fake' - or just for marketing?

First, your Pirelli's don't say max load XXXX at 51 psi. They say, max load XXXX, max pressure 51 psi. The max load occurs at 35 psi! And you're not supposed to use more than 51 psi when operated the tire.

And second, don't use that formula. It is based on a false assumption - that the max load is directly proportional to the pressure. It's not. It's PARTIALLY proportional to the pressure. I go into detail here:

http://www.barrystiretech.com/loadtables.html

Use a table.

No, don't use that formula at all. Use a load table. That may require you to do some searching on the 'net to find one - and the good news is that it doesn't matter what tire manufacturer publishes the table, they are merely reproducing the table published by the tire standardizing organizations - which apply to every tire manufacturer.



In this case you only need to find a table that has 225/50R17 in it. The load index and speed rating don't matter. (OK, there is one hiccup and that is you have to pay attention if the tire is SL (Standard Load) or XL (Extra Load)

Besides, the pressure listed on your vehicle tire placard is applicable to your vehicle regardless - unless you change tire size. (and here you can tell if your vehicle requires an XL tire if the specified pressure is over 35 psi - with a couple of exceptions.)



First, your Pirelli's don't say max load XXXX at 51 psi. They say, max load XXXX, max pressure 51 psi. The max load occurs at 35 psi! And you're not supposed to use more than 51 psi when operated the tire.

And second, don't use that formula. It is based on a false assumption - that the max load is directly proportional to the pressure. It's not. It's PARTIALLY proportional to the pressure. I go into detail here:

http://www.barrystiretech.com/loadtables.html

Use a table.


I looked at the Toyo table in your link. There is a P225/50R17 there, but the load/speed idx = 93V. As far as my Pirellis are concerned, they are 94V, and these are THEIR WORDS - not mine:

" MAX LOAD 670 kg [1477 lbs] AT 350 kPA [51 psi] " (from the tire itself)

According to the Toyo Table, for the closest approximate max load for a size 225/50R17 tire - 1,433lbs - I should inflate to 35psi cold.

Now: I like how the car rides/handles at 32-33psi cold(one would think Honda knows what they're doing!), and I do not like how it feels at mid-30s(psi) or higher pressure - rough ride, twitchy steering. My wife and I, plus a well-stocked toolbox in the trunk, barely equal 350lbs. And that's on weekends. Weekdays, it's just me in the Accord going to my job.

Your assessment?

I looked at the Toyo table in your link. There is a P225/50R17 there, but the load/speed idx = 93V. As far as my Pirellis are concerned, they are 94V, and these are THEIR WORDS - not mine:

" MAX LOAD 670 kg [1477 lbs] AT 350 kPA [51 psi] " (from the tire itself)

According to the Toyo Table, for the closest approximate max load for a size 225/50R17 tire - 1,433lbs - I should inflate to 35psi cold. …..

First, I only partially understand why some tire manufacturers write this wrong, but they do - and technically it's not exactly wrong, just misleading.

Just like Toyo table indicates, the load carrying capacity maxes out at 35 psi (OK, because it's a European standard, the pressure is 250 kPa (kiloPascals) ~ 36.3 psi - so the load carrying capacity is slightly higher. In the big scheme of things, the difference between what the Toyo table says (which comes from The Tire and Rim Association (TRA) - the American standardizing organization) and the European standardizing organization (ETRTO) is trivial - they are for practical purposes the same.)

Further, the Pirelli tire is misleading because the load carrying capacity of the tire from 250 kPa to 350 kPa is also 670 kg. By writing it the wat they did, many folks have concluded that these tires would be different than if the tire was written to say " at 250 kPa" - and that would be incorrect.

So I understand what Pirelli (and others) are doing, but many folks don't and they draw wrong conclusions from it.

So why do we have American standards and European standards (and we have Japanese standards as well!) that are almost the same, and therefore confusing?

Historically, the world wasn't as connected when these things were set up so it didn't matter. But with the global nature of the tire industry and our ability to communicate, we are encountering these quirks of the past.

There is a program to globally harmonize tires - BUT - they can't undo the past. Just a few weeks ago, I got my 2020 TRA yearbook and noticed that some passenger car tire sizes have a note to that effect.

…...Now: I like how the car rides/handles at 32-33psi cold(one would think Honda knows what they're doing!), and I do not like how it feels at mid-30s(psi) or higher pressure - rough ride, twitchy steering. My wife and I, plus a well-stocked toolbox in the trunk, barely equal 350lbs. And that's on weekends. Weekdays, it's just me in the Accord going to my job.

Your assessment?

Tire designers can dial in a whole range "feel" to a tire.

When the vehicle engineers were designing your car, they specified the tire size and inflation pressure FIRST, then the ride engineers dialed in the tire feel, the spring rates, the shock damping rates that they felt the consumer wanted. It turns out for you, they were right - but for someone else, it might have been wrong. For example, I prefer a more crisper turn in than is the norm and I am willing to sacrifice the ride to get it. That usually means I use more inflation pressure than what the door sticker says.

First, I only partially understand why some tire manufacturers write this wrong, but they do - and technically it's not exactly wrong, just misleading.

Just like Toyo table indicates, the load carrying capacity maxes out at 35 psi (OK, because it's a European standard, the pressure is 250 kPa (kiloPascals) ~ 36.3 psi - so the load carrying capacity is slightly higher. In the big scheme of things, the difference between what the Toyo table says (which comes from The Tire and Rim Association (TRA) - the American standardizing organization) and the European standardizing organization (ETRTO) is trivial - they are for practical purposes the same.)

Further, the Pirelli tire is misleading because the load carrying capacity of the tire from 250 kPa to 350 kPa is also 670 kg. By writing it the wat they did, many folks have concluded that these tires would be different than if the tire was written to say " at 250 kPa" - and that would be incorrect.

So I understand what Pirelli (and others) are doing, but many folks don't and they draw wrong conclusions from it.

So why do we have American standards and European standards (and we have Japanese standards as well!) that are almost the same, and therefore confusing?

Historically, the world wasn't as connected when these things were set up so it didn't matter. But with the global nature of the tire industry and our ability to communicate, we are encountering these quirks of the past.

There is a program to globally harmonize tires - BUT - they can't undo the past. Just a few weeks ago, I got my 2020 TRA yearbook and noticed that some passenger car tire sizes have a note to that effect.



Tire designers can dial in a whole range "feel" to a tire.

When the vehicle engineers were designing your car, they specified the tire size and inflation pressure FIRST, then the ride engineers dialed in the tire feel, the spring rates, the shock damping rates that they felt the consumer wanted. It turns out for you, they were right - but for someone else, it might have been wrong. For example, I prefer a more crisper turn in than is the norm and I am willing to sacrifice the ride to get it. That usually means I use more inflation pressure than what the door sticker says.

"For example, I prefer a more crisper turn
in than is the norm and I am willing to sacrifice
the ride to get it. That usually means I use more
inflation pressure than what the door sticker
says."

So you're of the 'more-is-better' crowd! Well you're hardly alone.

I mentioned it somewhere a while ago, but drivers(at least U.S. ones) fall into three camps as far as tire pressures are concerned:

40/20/40%, respectively: Underinflated, at or close to Tire Placard, and lastly, above Tire Placard and up to Max on the Tire.

You probably couldn't tolerate my TV picture settings either: nothing higher than the mid-point, and all calibrated for accuracy, not flashy picture.

Setting things the 'way they're supposed to be' is a lonely proposition, for sure!

I would characterize my approach to inflation pressure as "slightly over is better than slightly under", but surveyors would classify my cars as "properly inflated".

And the impression I am getting is that since the advent of TPMS, the percent of cars with underinflated tires is around 25% - and perhaps less. Of course that depends on what "underinflated" means - and I use 10% as that value.

I would characterize my approach to inflation pressure as "slightly over is better than slightly under", but surveyors would classify my cars as "properly inflated".

And the impression I am getting is that since the advent of TPMS, the percent of cars with underinflated tires is around 25% - and perhaps less. Of course that depends on what "underinflated" means - and I use 10% as that value.

Inflating an OEM size tire to above the vehicle's Tire Placard "properly inflated"?

Inflating an OEM size tire to above the vehicle's Tire Placard "properly inflated"?

Is "properly inflated" within 3%? If not, what tolerance do you propose?

This is a great discussion. I usually go a few psi up from door sticker as it seems to give better wear.

"Twitchy" is a good description of how overinflated tires feel.

Thanks for the info on the H rated Explorer tires, CapriRacer...that was part of the story of which I was not aware.

This is a great discussion. I usually go a few psi up from door sticker as it seems to give better wear.

"Twitchy" is a good description of how overinflated tires feel.

Thanks for the info on the H rated Explorer tires, CapriRacer...that was part of the story of which I was not aware.


Most people do overinflate, to some degree or other. 'More-is-better' is contagious!

Personally, I run several gauges to eliminate a 'high-reader'(a gauge that reads high leads to under-inflation).

Unless I'm running a different size/duty tire, I inflate to what's supposed to be in there, or maybe +1psi during fall into winter.

Most people do overinflate, to some degree or other. 'More-is-better' is contagious!

Personally, I run several gauges to eliminate a 'high-reader'(a gauge that reads high leads to under-inflation).

Unless I'm running a different size/duty tire, I inflate to what's supposed to be in there, or maybe +1psi during fall into winter.

The problem here is that the temperature varies from day to day - and even within a day. How do you set the pressures for when you are going to be driving the car? My approach is a few psi over. That way I am never too low and I naturally prefer the crisper turn in.

The problem here is that the temperature varies from day to day - and even within a day. How do you set the pressures for when you are going to be driving the car? My approach is a few psi over. That way I am never too low and I naturally prefer the crisper turn in.

I overinflate the tires 5psi the night before, then set them to Tire Placard or +1psi over first thing early morning.

Repeat 2X every month.

Done!

When I see Bridgestone's 'Ecopia' tires on anything German with three letters in the name I scratch my head.